dbuxton13

Can anyone confirm if the brake-based application is "turned off" or simply not there with the mechanical sport-differential installed?

I get it that BBTV works as the "poor man's" version of altering torque, but applying any degree of brakes in a turn, especially when accelerating out of it, seems to be an ineffecient method and backwards from a performance standpoint. Also I don't like the idea of introducing uneven brake-wear to each set, while also accelerating brake-wear ahead of normal use.

I would hope that BBTV would be completely unnecessary with a sport-diff.

superswiss

It's still there even with the sport differential, but it has different thresholds. The sport differential will do most of the work and the selective wheel torque control (the official name for the brake-based torque vectoring) will help along if necessary.

Also from the owner's manual:

markcincinnati

The BBT and TV-diff work together. In fact, if you get the TV, you will have practically the maximum effect possible -- the two technologies provide the ideal situation for mitigation of understeer.

I've driven an S4 without TV and an S5 with TV back to back on the same road under the same conditions. At the time the BBTV was NOT part of the package. My belief is that the S5 was able to take corners at a slightly higher speed and that I could get on the throttle a moment earlier coming out of the curve.

My concern about my "test" was that the S5 has a shorter wheelbase and may be able to corner at a somewhat higher speed due to that fact alone -- although I do believe the TV-diff did raise the speed higher than the shortened wheelbase alone.

What I would urge someone to do to test this feature is the following:

Test two S4's -- one with and one without the TV-diff (and they need to both have either All-Season tires or Summer tires and same wheels) back to back, same road, same circumstances (same ambient temp, etc.)

Set the TV-diff via ADS anyway you want (I would guess a couple or three runs would make sense Comfort, Auto and Dynamic) -- also make all of the ADS settings the same or use the factory settings (not Individual). Then make the "run" a couple of times to get the feel of the road and the corner you want to use for your evaluation. My test included finding the speed (maximum) that I could take the corner without venturing out of my lane.

If the speed at which you can take the corner in lane is "XMPH" and you attempt the corner at "XMPH+YMPH" causes you to drift into the left lane (assuming the corner is a right, e.g.) back off until you find THE XMPH that you can just barely stay in lane. Repeat the run a couple of times once you find the terminal speed.

Then do the same thing again with the car that has the sport diff (I'd probably try this exercise in Comfort and Dynamic with more frequency than Auto -- but that's just me). If you do this with someone in the passenger seat, you may find your ability to "record" your results are facilitated since you can mind the road rather than mind the speedo.

In my case, in the example above, S4 without and S5 with (and neither with the BBTV), the S5's terminal speed was +5MPH higher. About 10%. I had my wife in the passenger seat watching the speed for me. I believe the S4 had a full tank and the S5 had perhaps a quarter of a tank.

To me, this number was significant, but when I read tests about the TV-diff, the numbers were always much smaller than 10% -- which I can only assume is because my test subjects were too dissimilar (the two cars had different brands/models of tires which could have impacted the test -- and I didn't bother to check tire pressure either.)

Despite the artificially high results I observed, I have to say I was so enamoured by the TV-diff, I swore to myselft I would configure my 2018 with one (they had been a stand-alone option before the B9's). Then came the order guide and the TV-diff was no longer offered, rather it was in a bundle. I did end up ordering two S4's, one with it and one without the sport package. The one with the sport package was Ibis white with the Magma red interior. The other one was Daytona Gray Pearl. After so many white cars in a row, I went ahead and took the Daytona Gray configuration -- encouraged by my wife and the article which showed the difference with and without the sport diff was in the single digits. Besides, according to my rep, the BBTV was "a partial step" that did help mitigate understeer.

My regret? Not getting the sport diff -- but my preffered method of getting it would be as a stand alone option as it is offered elsewhere. Yet, that regret is perhaps, if I am honest with myself, more emotional than practical based on my understanding and readings on the merits of the BBTV. But, the hell of it is, before any discount, the package on top of a car that before tax and discount ended up at $60,900. Another $2,500 would not have been a material expense. I tell myself I voted with my dollars -- I voted against the "package-ification" of configurations.

I showed them!

Ha!

NB: Please recall, however, that after 40 years of car "buying" I actually bought this one, rather than leasing -- and please remember the sense I got from the service dept was that the TV-diff was an expensive proposition after the factory warranty expires.

superswiss

There seems to be a lot of focus on going around a corner faster when discussing the sport differential. While that's one aspect of the sport differential, this is missing a major other point. The sport differential is also about how the car feels from behind the steering wheel. The overall driving dynamics at any speed. The fact that you don't have to cross your arms, because you rarely need to turn the steering wheel more than 90 degrees around corners as the sport differential helps rotating the car, or the fact that you can control your turning radius with the throttle as opposed to making steering corrections. Basically the driving dynamics are more closely to a rear wheel driven car. The Car and Driver article linked above is pretty good and tries to make a point of this. These are soft aspects of the sport differential that for some people are more important than going around a corner a few mph faster. I'm one of them and it's why I keep Drive Select in Individual mode with my sport diff in Dynamic mode most of the time. The sport differential makes the car more controllable, more dynamic, more agile and more fun at any speed not just when going ***** out around a corner. Anybody who has ever owned an RWD car will greatly appreciate what the sport differential adds to this platforms. Those who don't know the difference between FWD, AWD w/o torque vectoring diffs and RWD driving dynamics probably won't appreciate what the sport diff has to offer, but just focusing on going faster around a corner misses a big aspect of it.

Now, the important point here is that you need to drive the car properly in order to experience these aspects. An understeering FWD or forward biased AWD car needs to be driven differently than an oversteering RWD or rear biased AWD car. Learn some driving techniques such as trail braking and throttle steering to really experience the difference between these layouts. You can do this w/o having to go to the track. Find some curvy road or even around town and start to use the throttle to control your turning radius (reduce throttle to widen and increase throttle to tighten) instead of making corrections with the steering wheel etc.

markcincinnati

superswiss: I 98.5% agree with what you said. It is the "soft" aspects of the TV-diff that I had longed for -- I had a 2012 SH-AWD equipped Acura TL Advance. I could -- via the graphical read-out -- actually both "see" and feel the impact of the TV diff in the Acura (which as you perhaps know, is even worse in terms of weight on the nose than the S4.) In the case of the Acura, pressing down on the accelerator while cornering gave me what I call the "hand of god" sensation -- meaning that just as I thought the Acura would "plow" due to its porky front end, an unseen (but felt) force would grab the rear of the car and "bend" it through the curve.

Overall, however, my sense was that the real "feel" (and this was bourne out on my S5 test drive) of the TV-diff was either at pretty high speeds or at least high g-forces. My attempt to explain the feeling via cornering yields a summary: If the road says it is nominally designed to have it navigated at 15MPH, the TV-diff can be felt at relatively low speeds (perhaps "felt" at 35MPH). If the road says "45MPH" the sport diff seems noticable once speed exceeds 70MPH.

Here's how I cam about this conclusion: I took Audi's Driver Training (on ice) four times and BMW's "X" training (on wet concrete) once.

I asked the Audi folks (the first time) why the driving capability school was taught on ice since everything we learned to do was -- by necessity -- at relatively low speeds. The Audi instructors told me, that giving the class on ABS, ESP, understeering, oversteering, steering "into a skid" and several other "racing techniques" on ice allows students to experience the exact same effect that would happen at very high speeds on dry pavement. We could induce a 360 spin as low as 20MPH on ice, whereas the exact same "laws of physics" if attempted on completely dry pavement would perhaps have to take place at 60, 70 or 80MPH to evoke the same behavior from the car. The risk (and cost of rubber and bent metal) was very high if the behavior was attempted on a dry concrete pad.

Likewise, BMW did very much the same in-car classroom training in BMW's with AWD (hence the name "X" training) on a concrete pad being continuously flooded with water (to evoke "out of control" circumstances) so that the student could learn to "steer into a skid" at perhaps 30MPH rather than at 60MPH or higher speeds on dry concrete.

The "muscle training" (and hopefully the muscle memory students develop) is the same at 20MPH on ice at it would be at 80MPH on asphalt -- the car responds identically, but on ice (or water) the training can happen without much danger when (notice I did not say "if") the student inevitably loses control of a car that is spinning. I did figure, too, that insurance costs, lawyer's guidance and the costs of tires (daily), wheel alignments and brake replacements required if the courses were given on dry pavement made attempting such training on dry pavement much too expensive a proposition.

I simply extrapolated, that to really get a lot out of a TV-diff would require relatively high speeds and risks to "my" tires, brakes and perhaps sheet metal. Driving on the curvy road (in an Audi S4 -- which does have, even without the TV-diff, already very high handling capabilities) has always seemed to require much higher speeds if one wants to "feel" the TV-diff than is typically prudent on public roads. Driving on the curvy road with a posted 45MPH "suggestion" at 75MPH is certainly possible with an S4, but I've found it risky to do so. Therefore, for me, the BBTV has provided my left brain with what it needs -- even though my right brain wants to crank it to 90MPH (which the S4 is quite willing and able to do) in order to get the "hand of god" feeling in an Audi (with its higher "native" talents, when compared with an Acura TL SH-AWD).

I live -- or would if I had ticked off the sport options -- for the soft aspects of the TV-diff. If you are only interested in it's ability to improve cornering and do not plan to take the car on the track, you might find the TV-diff option not as impressive as you might have hoped. And, to make this decision perhaps somewhat more difficult for a new Audi "shopper" who might become a "buyer," we have the perspective from Automobile magazine ". . . [Audi's] stealthy brake-actuated torque vectoring banishes the A4’s once much-loathed understeer into oblivion." Reviews of the RS3, too, do practically nothing to discourage one's thinking that the brake-based torque vectoring is THE ONE AND ONLY ONE TO HAVE.

I still want it (the sport diff); it's just that it is a lot more difficult to describe and demonstrate its "value" in improving the experience of driving a new B9 S4. I know what it is, it is the "je ne sais quoi option": That undefinable something; a quality that is, no matter how hard we try, indescribable. Whoever posted that C&D article didn't help much either (no offense). I mean all it did was say that it allowed the average speed on a slalom course to increase from 42.2mph to 42.7mph (and in the case of the Lexus they tested the cost to actually get the TV-diff was over $6,000 minimum). While I would pay for Audi's TV-diff (which was, until this year, $1,100), I'm not so sure there is anything other than "the undefinable something" to recommend it in the Lexus case. In the example of the Lexus, buying the option seems, well, dumb.

Twowheelsgood

It's too bad the diff wasn't a offered as standalone option for the B9 like it was for the B8. When I bought my first one in 2010, I got the diff but not the shocks. I never swapped out the OEM shocks but for anyone thinking of doing that, spending extra money for electronically controlled dampers and then tossing them out must have hurt. I certainly wouldn't have paid extra for red painted calipers as a standalone even though they're so much more effective than the same unit painted black that they're banned in F1. Something about interfering with the rotational inertia of the planet. I ignored all that and got the S-Sport package for the B9, mainly for the diff.

dbuxton13

Superswiss is hitting the nail on the head with his description here. Playing with the sport-diff through the throttle is an aspect of it that slaps a grin on my face, and just one of the reasons I personally would not consider buying an S car without it. I also feel strongly that all 3 of the advanced systems should be coupled together to work best in concert: sport-differential, sport suspension, and dynamic steering. Take any one or two of these away and, while the car is obviously still drivable, it is now missing the full effect those brilliant Audi engineers have cooked up for us operators.

For anyone who hasn't yet taken the time to read through the excellently descriptive article from Audi that Superswiss has linked a few times in this forum (https://www.audiworld.com/articles/q...ism-redefined/), allow me to abbreviate some key points from it:

--The sport differential takes effect not only under load, but also on the overrun; its torque distributing action even enhances the car’s agility when the clutch is disengaged

-- Depending on steering angle, lateral acceleration, yaw angle, road speed and other signals, the control unit calculates the most suitable distribution of torque to the wheels for every driving situation

--The difference in tractive force between the left and right wheels also exerts a steering effect, so that the usual corrections by the driver at the steering wheel are no longer needed

--The sport differential redistributes the power input continually with great rapidity and counteracts any tendency for the car to understeer or oversteer before either of these effects can build up. For the driver, this means reduced effort at the steering wheel and higher maximum lateral acceleration

--Since its reaction time is extremely short – less than 100 milliseconds – the sport differential takes effect even more rapidly than ESP

--ESP can only react to a discrepancy between the car’s steering angle and its actual body rotation, whereas the sport differential influences the car’s dynamic behaviour before any such discrepancies occur

--Actual road dynamics and those sensed subjectively by the driver are both enhanced, and driving pleasure benefits too, since ESP comes into action much less frequently

--It is capable of completely eliminating the classic load-reversal reactions when the accelerator is lifted or the brakes applied suddenly while cornering... if the accelerator pedal is released, torque distribution between the wheels is adjusted almost instantaneously

--Is just as effective when the engine is driving the wheels as it is on the overrun or when the car is coasting freely

--The computer obtains the information it needs from the steering angle, wheel speed, lateral acceleration and yaw-rate sensors and from current engine data... twin yaw-rate and lateral acceleration sensors are installed for the sport differential

-- The system has extremely high reaction speed: data from both sensors are continuously compared in the control unit, so that reliable results are available more rapidly

***Combined with the sport suspension (electronic damping control):

--At a cycle frequency of 1000 per second, the control unit computes the optimal damping force... the electromagnetically controlled valve selects a damping characteristic to match the current driving situation at any given moment

***Combined with dynamic steering:

--Can correct a small to moderate angle of float as rapidly and effectively as a rally driver could ever react, by automatically turning the wheels slightly in the opposite direction... brake applications are normally only needed if the angle is greater, and then in most cases only to exert a damping effect

--The dynamic steering system, damping control and sport differential work closely together with the ESP. They reduce the burden on the stabilisation program because the corrections take place considerably earlier via the input torque, the damping force or the steering angle. These rapid, efficient interventions avoid the need for brake applications in many cases, so that the car can be driven more dynamically and smoothly

**********

For anyone still in the research phase before buying this car, I think these are important considerations to keep in mind when weighing the option packages. The literature would disagree with any assessment that the sport-diff and other systems are only used "within 99% of the limit", but rather at varying levels for any scenario, and play a particularly important role in safe driving and recoveries.